Loving the Prophet (salla Allah alayhi wa sallam) is a necessary requirement of Iman. Defending his honor is a sign of belief. This is done by following his teachings and practice, not by murdering in his name.
Our Prophet was verbally abused and physically harrased multiple times in Makkah. Never ONCE did any of the Companions go and murder those who did such deeds.
Do those who kill others in the name of the Prophet believe that they love him more than the companions?
And even for those who believe that the penalty for blasphemy should be death: by unanimous consensus of ALL the scholars of Islam, this must take place after a legitimate trial, by a qualified judge, appointed by a legitimate Islamic state. Under NO circumstances does Islam allow vigilante justice, for to open this door leads to chaos, confusion and bloodshed.
Muslims: get your act together!! Such acts of terror are not only haram and spill innocent blood, they will come back to harm you and your communities in the short and long run.
And as a result, all of us will suffer.